CN108738342B

CN108738342B - Method for detecting fibre misalignment in an elongate structure, related device

Info

Publication number: CN108738342B
Application number: CN201680082490.1A
Authority: CN
Inventors: L.尼尔森; K.贾斯普尔森
Original assignee: LM WP Patent Holdings AS
Current assignee: LM WP Patent Holdings AS
Priority date: 2015-12-23
Filing date: 2016-12-19
Publication date: 2021-10-26
Anticipated expiration: 2036-12-19
Also published as: EP3394601A1; DK3394601T3; WO2017108689A1; MA44109A; CN108738342A; EP3394601B1; US10782128B2; US20190011254A1

Abstract

The present disclosure relates to a method for detecting fiber misalignment in an elongated structure, such as a wind turbine blade component. The elongated structure has a length along a longitudinal direction and comprises a plurality of stacked layers of reinforcing fibers. The plurality of fibrous layers includes fibers having an orientation that is substantially unidirectionally aligned in a longitudinal direction. The method includes scanning the elongated structure along at least a portion of the length by emitting an x-ray beam at an angle compared to the orientation of the fibers. The method includes detecting scattered radiation and determining an intensity of the detected scattered radiation. The method includes estimating a magnitude of the fiber misalignment based on the determined intensity.

Description

Method for detecting fibre misalignment in an elongate structure, related device

Technical Field

The present disclosure is in the field of composite structures, and more particularly relates to fiber misalignment in elongated structures. The present disclosure relates to methods for detecting fiber misalignment in elongated structures, and related devices.

Background

Fiber reinforced materials can be used to make elongated structures such as wind turbine blades, aircraft wings and boat hulls. The fibre reinforcement material is typically stacked to form a plurality of stacked layers, with the orientation of the fibres being aligned with the longitudinal direction of the elongate structure so as to provide stiffness in the longitudinal direction. The alignment of the stacked fiber layers is critical to the reliability and strength of the elongated structure. Any fiber misalignment may lead to failure or breakage of the wind turbine blade. Thus, identifying fiber misalignment or buckling (e.g. in-plane or out-of-plane misalignment) is necessary to correct the fiber misalignment and thereby ensure the reliability of the wind turbine blade. Knowing whether a fiber misalignment defect is present in the elongated structure and being able to quantify the defect using its location allows participation in appropriate repair work (such as grinding away the fiber misalignment and replacing the ground portion) and thereby eliminates excessive repair work. Furthermore, fiber misalignment detection provides higher reliability of the manufactured wind turbine blade, while also providing enhanced safety.

Now, fiber misalignment is detected by visual inspection on the surface of the elongated structure with a flash lamp and quantified using very simple tools (such as a crumple comb and ruler) when misalignment is observed. This visual inspection is inadequate because it only allows the detection of fiber misalignment present on the surface of the elongated structure. Not only fiber misalignment on the surface (such as deeper fiber misalignment or hidden fiber misalignment) is equally detrimental to the reliability of the elongated structure.

The ultrasonic detection method has not been fully proven to be useful as a method of identifying and quantifying wrinkles. The ultrasonic inspection method requires the addition of special materials for detecting misalignment, which may contaminate the surface of the blade, in order to provide a contact surface between the sensor and the object to be inspected. Furthermore, the sensor operates at wavelengths where proper detection or quantification of wrinkles cannot be achieved.

Accordingly, there is a need for a solution to detect fiber misalignment that is not on the surface of the elongated structure and/or to enable further quantification without the need for additional material.

Disclosure of Invention

It is an object of the present disclosure to provide a method for detecting fibre misalignment and which overcomes or ameliorates at least one of the disadvantages of the prior art or which provides a useful alternative.

One advantage of the present disclosure is that fiber misalignment below the surface can be detected by x-ray scanning and thus the elongated structure does not have to be damaged. This results in savings in repair time and cost. The present disclosure allows for detection and location of fiber misalignment over the depth of the elongated structure and thus eases repair work. Once the fiber misalignment is located, it can be repaired, which results in a significant reduction of such defects in the elongated structure. When the elongated structure is a wind turbine blade, this reduces the likelihood of failure and thus significantly improves the reliability of the wind turbine blade. Surprisingly, x-ray scanning has been found to be particularly useful for detecting misalignments in unidirectional fiber layers, as the detected signal will be significantly affected by the misalignment. Furthermore, surprisingly, x-ray scanning has been found to be particularly useful for detecting misalignments in a fibre layer comprising carbon fibres, which may be difficult to distinguish from the polymer matrix of the composite structure in other scanning methods.

The present disclosure relates to a method of manufacturing an elongated composite structure of fibrous composite material. The fiber composite includes reinforcing fibers embedded in a polymer matrix by using a mold having a length along a longitudinal direction. The method comprises the following steps: i) stacking a plurality of fiber layers in a mold, wherein the plurality of fiber layers comprise fibers having an orientation that is substantially unidirectionally aligned in a longitudinal direction; ii) supplying a liquid resin to the fibre layer, and iii) curing the resin to provide an elongate composite structure. The method is characterized by comprising the step of detecting fiber misalignment by using any of the steps disclosed herein.

The present disclosure relates to a fiber misalignment detection device. The fiber misalignment detection apparatus includes an x-ray beam emission module configured to scan the elongated structure along at least a portion of the length by emitting an x-ray beam at an angle compared to the longitudinal direction. The fiber misalignment detection apparatus includes an x-ray detector module configured to detect scattered radiation. The fiber misalignment detection apparatus includes a processing module configured to: determining the intensity of the detected scattered radiation; and estimating a magnitude of the fiber misalignment based on the determined intensity.

According to another aspect, the invention provides a fibrous reinforcement material comprising carbon fibers and a plurality of tracer yarns (tracer yarns) made of a second type of material, such as glass fibers. The fiber reinforcement layer material may for example comprise a plurality of carbon fiber filaments and a number of tracer yarns. The tracer yarn can be made of glass fibers, for example, and can be embodied as a glass fiber roving, for example. The fibrous reinforcement layer may comprise predominantly unidirectional fibres. Accordingly, tracer yarns (e.g., glass fiber rovings) may provide better detection of possible wrinkles in splices (layups) that are not typically detectable in pure carbon fiber splices. The fiber volume content of the second type of material may be less than 10%, such as less than 7.5%, or even less than 5%. In other words, the carbon fiber content may also be at least 90%, such as at least 92.5% or even at least 95%.

It will be apparent that the aforementioned aspects of the invention may be combined in any manner and linked by a common aspect of detecting fibre misalignment in an elongate structure.

It is noted that the advantages elucidated with respect to the method of detecting fibre misalignment apply to the method of manufacturing an elongated composite structure as well as to the fibre misalignment detection apparatus.

Drawings

Embodiments of the invention will be described in more detail below with respect to the accompanying drawings. The drawing shows one way of implementing the invention and is not to be construed as limiting the other possible embodiments falling within the scope of the appended set of claims.

FIG. 1 is a schematic diagram illustrating an exemplary wind turbine blade according to some aspects of the present disclosure;

FIG. 2 is a schematic diagram illustrating an exemplary cross-section of a wind turbine blade according to aspects of the present invention;

3-4 are schematic diagrams illustrating different views of exemplary fiber misalignment in exemplary elongated structures according to aspects of the present disclosure;

FIG. 5 is a flow chart illustrating an exemplary method for detecting fiber misalignment in an elongated structure, according to some aspects of the present disclosure;

FIG. 6 is a flow diagram illustrating an exemplary method for fabricating an elongated composite structure according to some aspects of the present disclosure;

FIG. 7 is a block diagram illustrating an exemplary fiber misalignment detection arrangement according to some aspects of the present disclosure; and

8a-b are diagrams illustrating an exemplary fiber misalignment detection device according to embodiments of the invention.

Detailed Description

As set forth in the background, there is a need for a method for detecting fiber misalignment, such as identifying hidden (below surface) fiber misalignment, in an efficient and non-destructive manner. Inspection based on simple visual "flashlights" is non-destructive, but does not allow identification of fiber misalignment beneath the surface of the elongated structure. X-ray based inspection allows for non-destructive detection of fiber misalignment that cannot be visually detected. However, when used conventionally (i.e. at high power, e.g. 120kV or higher), x-ray radiation provides full tomography of the object under examination. In this disclosure, detecting the presence of fiber misalignment in an elongated structure may be sufficient to perform repair work. The present disclosure proposes an unconventional use of x-ray scanning configured to provide for detecting misalignment without full tomography (and optionally misaligned full tomography). The present disclosure thus advantageously provides a non-destructive detection of fiber misalignment by irradiating an elongated structure with x-rays, collecting reflected or scattered radiation, and identifying fiber misalignment based on the intensity of the reflected or scattered radiation.

The present invention relates to a method for detecting fibre misalignment in an elongate structure, such as a wind turbine blade component, an aircraft wing or a hull of a vessel. It is evident that the invention is particularly suitable for large elongated structures where non-destructive inspection is highly appreciated due to the costs incurred by destructive inspection. The invention thus preferably relates to a wind turbine blade and an intermediate elongated structure having a total length of at least 30 meters, 40 meters, 45 meters or 50 meters and a thickness of 1-80 mm. Thus, the present invention preferably relates to wind turbine blades comprising materials with different densities, such that x-ray radiation may show misalignment.

Fiber misalignment herein refers to misalignment between two or more fiber layers, which may mean deviation from the plane of the fibers (such as out-of-plane misalignment) or deviation in a transverse manner within the plan view of the fibers (such as in-plane misalignment). In-plane misalignment is theoretically as severe as out-of-plane misalignment, but is less likely. In-plane misalignment is primarily reduced and remedied by the construction of the material layers making up the fibrous layers. However, in-plane misalignment does not affect the plurality of plies as does out-of-plane misalignment. Examples are fiber misalignments being wrinkles, undulations, folds, wrinkles, etc.

The elongated structure has a length along a longitudinal direction and comprises a plurality of stacked layers of reinforcing fibers. The plurality of stacked layers of reinforcing fibers includes fibers having an orientation that is unidirectional and substantially aligned in a longitudinal direction. The longitudinal direction may be defined as a direction along the length of the elongated structure, such as forming a root end of the elongated structure towards a tip end of the structure (e.g. towards a tip end of the wind turbine blade). The plurality of fibrous layers are aligned (predominantly) in one direction substantially parallel to the longitudinal direction. The fibre layers are thus substantially unidirectional in the longitudinal direction. The reinforcing fiber layer may consist essentially of carbon fibers and/or glass fibers. According to an advantageous embodiment, the reinforcing fiber layer comprises at least 25%, or at least 30%, or at least 35%, or at least 40%, or at least 50%, or at least 60%, or at least 70%, or at least 80%, or at least 90% carbon fibers. The reinforcing fibre layer may even consist entirely of carbon fibres.

The method includes scanning the elongated structure along at least a portion of the length by emitting an x-ray beam at an angle compared to the orientation of the fiber, such as by moving a fiber misalignment detection device along at least a portion of the length and emitting the x-ray beam at an angle compared to the orientation of the fiber. For example, the fiber misalignment detection device moves along at least a portion of the length (e.g., in translational movement in a longitudinal direction) while emitting an x-ray beam at an angle compared to the orientation of the fibers.

The method includes scanning the elongated structure along at least a portion of the length by emitting an x-ray beam at an angle compared to the orientation of the fibers, such as emitting the x-ray beam toward the elongated structure at a predetermined angle compared to the orientation of the fibers. The detector device is advantageously arranged to detect backscattered or reflected x-rays. The angle is formed, for example, with respect to a plane indicating the orientation of the fibers, such as a longitudinal plane substantially parallel to the longitudinal direction. The fibers may be oriented parallel to the surface of the elongated structure; the x-ray beam may thereby be conveyed or directed toward the surface at an angle formed with respect to the surface. When the surface is curved, the x-ray beam may be directed toward the surface at an angle formed with respect to a plane tangential to the surface. Out-of-plane and/or in-plane fiber misalignment can be detected in terms of the angle and direction of x-ray emission toward the elongated structure. For example, to detect in-plane fiber misalignment, scanning is performed at an angle compared to a plane substantially orthogonal to the fiber orientation. According to some aspects of this disclosure, the angle is a shallow angle of between about 0.5 degrees and about 45 degrees with respect to the plane of the fiber layer (such as between about 0.5 degrees and about 20 degrees with respect to the plane of the fiber layer, such as between about 0.5 degrees and about 15 degrees with respect to the plane of the fiber layer). It should be noted that the plane of the fibre layer may be curved along the structure, for example if the structure is a shell part for bending or pre-bending a wind turbine blade.

In other words, emitting the x-ray beam includes irradiating or exposing the elongated structure with the x-ray beam. The x-ray beam is generated by an x-ray emission source (e.g., an x-ray tube or an x-ray generator) configured to emit the x-ray beam at a wavelength ranging from 0.01 nanometers to 10 nanometers, or at a frequency ranging from 30 gigahertz to 30 gigamegahertz, or at an energy level in the range of 100eV to 150 keV. According to one or more advantageous embodiments, the x-ray beam is emitted at an energy level in the range of 5keV-120 keV. The x-ray emission source may be operated at 5-120keV and 25-100 muA.

The method includes detecting scattered radiation, such as radiation scattered by and reflected by the elongated structure. For example, an x-ray emission source projects an x-ray beam toward an elongated structure. The x-ray beam is scattered: some of the x-ray beams pass through the elongated structure, some are reflected and some are absorbed. The resulting pattern of scans (and radiation) is then ultimately detected by a detection medium, such as an x-ray detector module or a backscatter detection module. In other words, detecting scattered radiation includes detecting reflected radiation and/or passing radiation. The resulting pattern of the scan depends on the material properties, such as density, of the elongated structures. For example, when the elongated structure comprises a resin and a plurality of stacked layers of reinforcing fibers made of carbon fibers and glass fibers, the x-rays are scattered (e.g. reflected, passed through, absorbed) by the resin (e.g. polyester matrix or vinyl matrix) and the carbon fibers, since the difference in electron density is different from that by the glass fibers, and thus detecting the scattered rays provides a distinction between carbon fibers and glass fibers, since the density of the glass is different from that of the carbon. Misalignment of the glass fibers can thus be detected according to this disclosure and thus show fiber misalignment of any fibers within the stacked layers of reinforcing fibers.

The method includes determining an intensity of the detected scattered radiation. Stated differently, the method includes measuring an intensity of the detected scattered radiation, such as an energy reflected by the radiation in, for example, electron volts (such as a magnitude or level of the reflected radiation).

The method includes estimating a magnitude of the fiber misalignment based on the determined intensity. In other words, the method comprises determining whether a fiber misalignment to be repaired is present in the elongated structure, e.g. whether a non-negligible fiber misalignment is present in the elongated structure. According to some aspects of this disclosure, the step of estimating a magnitude of the fiber misalignment based on the determined intensity includes estimating a magnitude of the out-of-plane fiber misalignment. The magnitude of the fiber misalignment herein refers to a quantitative measure characterizing the misalignment, such as the height of the misalignment, the deviation angle of the misalignment with respect to the aligned fibers, and/or the location of the misalignment across the thickness of the elongated structure. According to some aspects of the disclosure, estimating the magnitude of the fiber misalignment based on the determined intensity includes determining whether the determined intensity is above an intensity threshold, and detecting a fiber misalignment to repair when the determined intensity is determined to be above the intensity threshold. When the determined intensity is not determined to be above the intensity threshold, then the fiber misalignment is considered negligible or non-existent. For example, when the determined intensity or intensity difference is above a threshold showing a non-negligible deviation in terms of photon counting, a fiber misalignment is detected and positioned for repair. According to some aspects of the present disclosure, the method further includes positioning the fiber misalignment within the elongated structure to effect the repair. Locating the fiber misalignment includes, for example, determining the depth from the surface (e.g., mm or number of layers/plies) at which the fiber misalignment is located, and/or locating the position of the fiber misalignment in the length of the elongated structure (such as the distance from both edges of the elongated structure). The x-ray radiation depends on the number of x-ray detector modules involved, the exposure time (i.e. the time it takes to irradiate a given surface), and the energy level of the radiation. Thus, it is contemplated that the elongated structure is first irradiated or scanned at a low energy level (e.g., 80keV) for a short period of time (e.g., 1h for the entire elongated structure) to reveal a misalignment of a certain size (e.g., 3 degrees) and then irradiated or scanned at a higher energy level (e.g., 120 keV) for a longer period of time (e.g., more than 1h for the entire elongated structure) to further characterize the depth and size of the same misalignment. The higher energy level does not exceed a certain level above which it does not comply with safety regulations.

According to some aspects of the disclosure, estimating a magnitude of the fiber misalignment based on the determined intensity includes determining whether the determined intensity substantially matches a predetermined intensity level corresponding to a type of fiber misalignment, and when it is determined that the determined intensity substantially matches the predetermined intensity level, classifying the fiber misalignment in the corresponding type. One type of fiber misalignment is characterized, for example, by its size, which can be detected using a characterization energy level (or energy range) or exposure time (or exposure time range). When the determined intensity is not determined to substantially match a predetermined intensity level corresponding to a type of fiber misalignment, the fiber misalignment is not classified and may be negligible. The predetermined intensity level includes signatures (signatures) characterizing fiber misalignment in terms of angle, depth, ply geometry, partial tomography, and the like.

According to some aspects of this disclosure, the step of emitting the x-ray beam at an angle includes emitting the x-ray beam through a collimator and/or emitting the x-ray beam with low power (such as 60kW or less). For example, emitting an x-ray beam through a collimator includes emitting the x-ray beam along a region, line, and/or plane defined by the collimator in order to narrow the beam, i.e., to urge the direction of the beam to align more and more toward the same direction. Thereby, the fiber layers are radiated along well-defined lines and planes, whereby the position of possible fiber misalignment can be determined. The scattered signal may be detected, for example, via a detector device having a pinhole, whereby x-rays scattered from a well-defined location will be emitted to a specific detector.

Emitting the x-ray beam with the reduced power includes emitting the x-ray beam with a power equal to or less than 60kW (such as less than 40kW, such as less than 10kW, such as 5 kW). This allows to confine the x-ray radiation to a local area and thus makes the solution disclosed herein suitable for proper shielding or protection to reduce absorption by nearby body tissue.

According to some aspects of the disclosure, the method further comprises scanning the elongated structure along at least a portion of the length by emitting additional x-ray beams at additional angles. The additional x-ray beam may, for example, be directed in the opposite direction of the first x-ray beam (e.g., at an additional angle of 180-alpha, alpha being the first angle). This has the advantage that the detection method can detect both out-of-plane misalignments or fluctuations at both positive and negative angles simultaneously. It is of course also possible to perform the scan in two steps by first performing the scan with an x-ray beam oriented at a first angle and later performing a second scan with an x-ray beam oriented at a second angle, e.g. the inverse of the first angle. Additionally or alternatively, the method further comprises scanning the elongated structure along at least a portion of its length by emitting second signals/rays at a plurality of angles so as to obtain a 3D representation of the fibre misalignment.

In one or more embodiments of the present disclosure, the step of scanning and/or the step of estimating occurs before and/or after an infusion phase before and/or after a curing phase. This infusion phase corresponds to the phase of resin infusion on the layer of fibres forming the elongated structure. This curing phase corresponds to the phase after infusion, where the infused fibrous layer hardens.

In one or more embodiments of the present disclosure, the plurality of stacked reinforcement fiber layers includes a carbon fiber layer, or a carbon fiber layer and a glass fiber layer. When the plurality of stacked reinforcement fiber layers includes carbon fiber layers and glass fiber layers, estimating a magnitude of the fiber misalignment includes estimating a magnitude of the glass fiber misalignment. Because it is not easy to distinguish between carbon fiber layers and resin after infusion and carbon fiber layers are aligned with glass fiber layers, glass fiber is one of the media of a size that can then help estimate any kind of fiber misalignment.

In one or more embodiments of the present disclosure, the plurality of stacked reinforcement fiber layers includes a carbon fiber layer having tracer yarns. For example, in portions of the elongated structure made of carbon and resin, x-ray scanning does not allow for identifying misalignments. However, tracer yarns incorporated in multiple stacked layers of reinforcing fibers enable detection and estimation of misalignment. The tracer yarn may be made from any of a number of materials having a density substantially different from the density of the carbon or resin. For example, the tracer yarns may comprise glass. The tracer yarn may have a diameter matching the diameter of the carbon fibers.

In one or more embodiments of the present disclosure, the plurality of stacked layers of reinforcing fibers comprises 1 to 80 layers, such as up to 60 layers, such as up to 30 layers. The plurality of stacked layers of reinforcing fibres may have a total thickness of 1 to 80mm (such as 1-60mm, such as 1-30 mm).

According to some advantageous aspects, the elongated structure is a wind turbine blade component. The wind turbine blade component is a load bearing structure such as a main laminate (laminate) or spar cap of a wind turbine blade.

In one or more embodiments of the present disclosure, the method includes storing scans of the elongated structure in relation to the position (of the scanned fiber layer or x-ray system) in order to provide an overall view of the elongated structure and possible positions of fiber misalignment.

The present disclosure relates to a fiber misalignment detection device. The fiber misalignment detection apparatus includes an x-ray beam emission module configured to scan the elongated structure along at least a portion of the length by emitting an x-ray beam at an angle compared to the longitudinal direction. The x-ray beam emission module is for example an x-ray generator module capable of passing an x-ray beam or signal through an elongated structure at a given angle, for example by using a collimator or a slit. The x-ray beam emission module is, for example, configured to receive or derive an angle to be used for transmitting the x-ray beam, and to adjust the emission of the x-ray beam in accordance with the received or derived angle (such as adjusting a collimator of the x-ray emission module or a slit of the x-ray emission module accordingly). The collimator supports an aiming focus so that the x-ray detector module can detect or receive scattered radiation.

The fiber misalignment detection apparatus includes an x-ray detector module configured to detect scattered radiation.

The fiber misalignment detection apparatus includes a processing module configured to determine an intensity of detected scattered radiation; and estimating a magnitude of the fiber misalignment based on the determined intensity. The processing module comprises, for example, an intensity determiner module configured to determine an intensity of the detected scattered radiation and an estimator module configured to estimate a magnitude of the fiber misalignment based on the determined intensity.

In one or more embodiments of the fiber misalignment detection apparatus, the x-ray beam emission module includes a collimator and is configured to scan the elongated structure along at least a portion of the length by emitting an x-ray beam through the collimator at an angle compared to the longitudinal direction.

The fiber misalignment detection device is configured to move along at least a portion of the length of the elongated structure in the longitudinal direction while emitting an x-ray beam at an angle compared to the longitudinal direction by the collimator.

Fig. 1 shows a schematic view of a wind turbine blade 10. The wind turbine blade 10 has the shape of a conventional wind turbine blade and comprises a root region 30 closest to the hub of the wind turbine, a profile or airfoil region 34 furthest away from the hub, and a transition region 32 between the root region 30 and the airfoil region 34. The blade 10 comprises a leading edge 18 facing in the direction of rotation of the blade when the blade is mounted on the hub, and a trailing edge facing in the opposite direction to the leading edge 18. The wind turbine blade 10 has a length in the longitudinal direction of the blade indicated by an arrow showing the distance r.

The airfoil region 34 (also referred to as the profile region) has an ideal or almost ideal blade shape with respect to generating lift, while the root region 30 has a substantially circular or elliptical cross-section due to structural considerations, which for example makes it easier and safer to mount the blade 10 to the hub. The diameter (or chord) of the root zone 30 may be constant along the entire root zone 30. The transition region 32 has a transition profile that tapers from the circular or elliptical shape of the root region 30 to the airfoil profile of the airfoil region 34. The chord length of the transition zone 32 generally increases with increasing distance r from the hub. The airfoil region 34 has a chordal airfoil profile extending between the leading and trailing

edges

18, 18 of the blade 10. The width of the chord of the airfoil region 34 decreases with increasing distance r from the hub.

The shoulder 40 of the blade 10 is defined as the location where the blade 10 has its maximum chord length. The shoulder 40 is generally provided at the boundary between the transition region 32 and the airfoil region 34.

It should be noted that the chords of different sections of the blade usually do not lie in a common plane, since the blade may be twisted and/or bent (i.e. pre-bent), thus providing a corresponding twisting and/or bending process for the chord plane, which is most often the case in order to compensate for the local velocity of the blade depending on the radius from the hub.

The blade is typically made of a pressure side shell part 36 and a suction side shell part 38, which shell

parts

36, 38 are bonded to each other along bonding lines at the leading edge 18 and the trailing edge of the blade.

Fig. 2 shows a schematic view of a cross-section of the blade along the line l-l shown in fig. 1. As previously mentioned, the blade 10 includes a pressure side shell portion 36 and a suction side shell portion 38. The pressure side shell section 36 includes a spar cap 41 (also referred to as a main laminate) that forms the load carrying portion of the pressure side shell section 36. The spar cap or main laminate is an elongated structure, such as an elongated composite structure that may form a load carrying structure of a wind turbine blade. The spar cap 41 comprises a plurality of stacked layers 42 of reinforcing fibres, which mainly comprise unidirectional fibres aligned in the longitudinal direction of the blade in order to provide stiffness to the blade. The suction side shell part 38 further comprises a spar cap 45 (or main laminate corresponding to the elongated structure) comprising a plurality of stacked layers 46 of reinforcing fibers. The pressure side shell portion 38 may also include a sandwich core material 43, typically made of balsa wood or foamed polymer, sandwiched between a plurality of fiber reinforced skin layers. The sandwich core material 43 is used to provide stiffness to the shell to ensure that the shell substantially maintains its aerodynamic profile during rotation of the blade. Similarly, the suction side shell portion 38 may also include a sandwich core material 47.

The spar caps 41, 45 of the pressure side shell part 36 and the suction side shell part 38 are connected via a first shear web 50 and a second shear web 55. In the illustrated embodiment, the

shear webs

50, 55 are formed as substantially I-shaped webs. The first shear web 50 comprises a shear web body and two web foot flanges. The shear web body comprises a sandwich core material 51, such as balsa wood or foamed polymer, covered by a number of skin layers 52 made of a number of fibre layers. The secondary shear web 55 has a similar design to the shear web body comprising a sandwich core material 56 covered by a number of skin layers 57 made of a number of fibre layers and the two web foot flanges. The

sandwich core material

51, 56 of the two

shear webs

50, 55 may have a chamfer (chamferred) near the flange to transfer loads from the

webs

50, 55 to the

primary laminates

41, 45 without risk of failure and fracture at the joint between the shear web body and the web foot flange. However, such a design will typically create a resin rich area in the joint area between the leg and the flange. Further, such resin rich areas may include burning resin due to high exothermic peaks during the curing process of the resin, which in turn may lead to mechanical weakness.

To compensate for this, a number of filler strings 60 comprising glass fibers are typically arranged at these junction areas. Further, such cords 60 will also facilitate transferring loads from the skin layer of the shear web body to the flange. However, alternative construction designs are possible in accordance with the present invention.

The

blade shells

36, 38 may include additional fiber reinforcement at the leading and trailing edges. Typically, the

housing portions

36, 38 are bonded to one another via glue flanges in which additional filler strings (not shown) may be used. In addition, very long blades may comprise segment sections with additional spar caps, which are connected via one or more additional shear webs.

Fig. 3-4 are schematic diagrams illustrating different views of an exemplary fiber misalignment 302 in an exemplary elongated structure 300 according to some aspects of the invention. Fig. 3 shows a perspective view of an elongated structure 300 that allows visualizing a layer configuration of the elongated structure 300 comprising the occurrence of fiber misalignment. The exemplary elongated structure 300 includes a plurality of stacked layers 304 of reinforcing fibers. The plurality of stacked layers of reinforcing fibers 304 are unidirectional and are oriented substantially in a longitudinal direction indicated by arrow 306. Fig. 3 illustrates an exemplary out-of-plane fiber misalignment 302, where the fiber misalignment deviates from the fiber plane (defined as the plane formed by most of the same fiber layers) and distorts adjacent fiber layers, resulting in a defect in the elongated structure. Fig. 4 shows a cross-sectional view of an exemplary fiber misalignment 302 at an exemplary elongated structure 300. The elongated structure 300 has a thickness, indicated by h in fig. 4, ranging, for example, from 1mm to 80mm or any subrange therebetween. The plurality of stacked layers of reinforcing fibers 304 partially or entirely form the thickness of the elongated structure at the point of interest. The plurality of stacked layers of reinforcing fibers 304 are substantially unidirectional in a longitudinal direction indicated by arrow 306. This fiber misalignment 302 causes a deviation in the angle α and causes distortion on adjacent fiber layers. It facilitates the use of a number of layers or slabs in relation to the distance from or from the surface to be scanneddThe depth of the indicated fiber misalignment 302 is approximately located to prepare for repair accordingly. The x-ray scanning disclosed herein allows for detection of fiber misalignment 302 and quantification of the size of fiber misalignment 302 (which may be in terms of depth)dAngle alpha and/or position (e.g., longitudinal position or coordinates with respect to a reference point). Optionally, the methods disclosed herein using x-ray scanning provide an identification of the fiber misalignment 302, which can be estimated with respect to the geometry of the fiber misalignment 30 and/or the energy absorbed and/or the energy reflected back by the fiber misalignment 302. For example, exposing the elongated structure to x-rays at different angles allows identifying a match between the angle at which the x-ray beam is emitted (i.e., the emission angle) and the deviation angle α, i.e., the signal strength changes significantly when the emission angle and the deviation angle α are parallel.

Fig. 5 is a flow diagram illustrating an exemplary method 500 for detecting fiber misalignment in an elongated structure according to some aspects of the invention. The method 500 is targeted at detecting fiber misalignment in an elongated structure, such as a wind turbine blade component, an aircraft wing, or a hull of a ship. The method 500 addresses fiber misalignment including out-of-plane fiber misalignment and in-plane fiber misalignment. The elongated structure has a length along a longitudinal direction and comprises a plurality of stacked layers of reinforcing fibers. The plurality of stacked layers of reinforcing fibers comprise fibers having an orientation that is unidirectional and substantially aligned in a longitudinal direction.

The method comprises scanning S1 the elongated structure along at least a portion of the length by emitting an x-ray beam at an angle compared to the orientation of the fibers. The angle is formed, for example, with respect to a plane indicating the orientation of the fibers (such as a longitudinal plane substantially parallel to the longitudinal direction). The fibers may be oriented parallel to the surface of the elongated structure; the x-ray beam may thus be conveyed or directed towards the surface at an angle formed with respect to the surface. For example, scanning S1 includes emitting an x-ray beam toward the elongated structure at a predetermined angle compared to the orientation of the fibers by a backscatter x-ray device. According to some aspects of this disclosure, the angle is a shallow angle of between about 0.5 degrees and about 45 degrees with respect to the plane of the fiber layer (such as between about 0.5 degrees and about 20 degrees with respect to the plane of the fiber layer, such as between about 0.5 degrees and about 15 degrees with respect to the plane of the fiber layer). In other words, scanning S1 includes irradiating or exposing the elongated structure with an x-ray beam at a predefined angle to x-ray radiation while scanning the elongated structure. According to one or more advantageous embodiments, scanning S1 may include generating an x-ray beam using an x-ray emission source (e.g., an x-ray tube or an x-ray generator) configured to emit x-rays at an energy level in a range of 5keV-120 keV. The x-ray emission source may be operated at 5-120keV and 25-100 muA.

The method 500 includes detecting S2 scattered radiation, such as radiation scattered by and reflected by the elongated structure. For example, the x-ray beam is scattered: some of the x-ray beams pass through the elongated structure, some are reflected and some are absorbed. Detecting S2 scattered radiation is performed by a detection medium, such as an x-ray detector module or a backscatter detection module, capable of detecting the resulting pattern (and radiation) of the scan. In other words, detecting S2 scattered radiation includes detecting reflected radiation and/or passed radiation. Detecting S2 scattered radiation includes, for example, detecting radiation scattered through glass and/or carbon fibers, which is indicative of misalignment of the glass fibers. This allows any other fibers shown in this position to be misaligned within the stacked reinforcing fiber layer.

The method 500 includes determining S3 an intensity of the scattered radiation detected. For example, determining S3 the intensity includes measuring the intensity of the detected scattered radiation, such as the energy reflected by the radiation in, for example, electron volts (such as the magnitude or level of the reflected radiation).

The method 500 includes estimating S4a magnitude of the fiber misalignment based on the determined intensity. In other words, estimating the magnitude of the fiber misalignment of S4 includes determining whether there is a fiber misalignment to be repaired in the elongated structure, e.g., whether there is a non-negligible fiber misalignment in the elongated structure. In one or more embodiments, estimating S4 the magnitude of the fiber misalignment is actually a computational characterizationA quantitative measure of misalignment, such as the height of the misalignment, the deviation angle of the misalignment with respect to the aligned fibers, and/or the position of the misalignment across the thickness of the elongated structure. According to some aspects of the disclosure, estimating S4a magnitude of the fiber misalignment based on the determined intensity includes determining whether the determined intensity is above an intensity threshold S4a, and detecting the fiber misalignment to be repaired when the determined intensity is determined to be above the intensity threshold. When the determined intensity is not determined to be above the intensity threshold, then the fiber misalignment is considered negligible or non-existent. In an illustrative example where the present technique is applicable, the intensity threshold is related to photon counts, and in particular to the difference Δ in measured photon counts, such as the deviation in measured photon counts over a region compared to the remainder of the elongated structure or perfectly or ideally aligned elongated structure. When the determined intensity is above a threshold, a fiber misalignment is detected for repair. The method 500 may further proceed to determine the location of a fiber misalignment in the thickness of the stacked fiber layers by comparing the intensity of scattered radiation from aligned fibers immediately prior to the misalignment and the intensity of scattered radiation from aligned fibers at different angles. According to some aspects of the disclosure, the method 500 further includes locating S5 a fiber misalignment within the elongated structure to effect the repair. Locating the fiber misalignment S5 includes determining a depth from the surface (e.g., mm or number of layers/plies) at which the fiber misalignment is located, and/or a location along the length of the elongated structure at which the fiber misalignment is located. Referring to FIG. 4, locating S5 includes, for example, calculating a depthd。

According to some aspects of the disclosure, estimating S4a magnitude of the fiber misalignment based on the determined intensities includes determining whether the determined intensities of S4b substantially match a predetermined intensity level corresponding to a type of fiber misalignment, and when it is determined that the determined intensities substantially match the predetermined intensity level, classifying the fiber misalignment in the corresponding type. When the determined intensity is not determined to substantially match a predetermined intensity level corresponding to a type of fiber misalignment, the fiber misalignment is not classified and may be negligible or unknown. The predetermined intensity level includes signatures characterizing fiber misalignment in terms of angle, depth, ply geometry, partial tomography, and the like. In an illustrative example to which the disclosed invention is applicable, a predetermined intensity level of 80keV indicates a fiber misalignment of 3 degrees.

According to some aspects of this disclosure, the step S1 of scanning by emitting the x-ray beam at an angle includes emitting S1a the x-ray beam through a collimator and/or emitting the x-ray beam at a low power (such as 60kW or less). For example, emitting an x-ray beam through a collimator includes emitting the x-ray beam along a region, line, and/or plane defined by the collimator in order to narrow the beam, i.e., to urge the direction of the beam to align more and more toward the same direction. Emitting the x-ray beam with the reduced power includes emitting the x-ray beam with a power equal to or less than 60kW (such as less than 40kW, such as less than 10kW, such as 5 kW). This allows to confine the x-ray radiation to a local area and thus makes the solution disclosed herein suitable for proper shielding or protection to reduce absorption by nearby body tissue.

According to some aspects of the disclosure, the method 500 further includes scanning S6 the elongated structure along at least a portion of the length by emitting additional x-ray beams at additional angles. For example, S6 may include emitting additional x-ray beams in a direction opposite the first x-ray beam of step S1 (e.g., at an additional angle of 180- α, α being the first angle used in step S1). This has the advantage that the detection method 500 can detect both out-of-plane misalignments or fluctuations at both positive and negative angles. It is of course also possible to carry out the scan in two steps by first carrying out the scan with an x-ray beam oriented at a first angle, such as in step S1, and later carrying out a second scan with an x-ray beam oriented at a second angle, e.g. the inverse of the first angle, such as in step S6. Additionally or alternatively, the method 500 further comprises scanning the elongated structure I along at least a portion of its length by emitting second signals/rays at a plurality of angles in order to obtain a 3D representation of fiber misalignment or full tomography of fiber misalignment.

In one or more embodiments of the present disclosure, the method 500 may include integrating tracer yarns in a plurality of stacked layers of reinforcing fibers, and wherein estimating a magnitude of the fiber misalignment of S4 includes estimating a magnitude of the tracer yarn misalignment.

Fig. 6 shows a flow diagram illustrating an exemplary method 600 for fabricating an elongated composite structure according to some aspects of the present invention. The method relates to an elongated composite structure of a fibrous composite material. The fiber composite includes reinforcing fibers embedded in a polymer matrix by using a mold having a length along a longitudinal direction. The method 600 includes the steps of:

-i) stacking Sx1 multiple fiber layers in a mould, wherein the multiple fiber layers comprise fibers having an orientation substantially (unidirectionally) aligned in a longitudinal direction;

ii) supplying Sx2 liquid resin to the fibre layer, and

-iii) curing the resin with Sx3 to provide an elongated composite structure.

The method 600 advantageously further includes detecting Sx4 fiber misalignment using any of the steps of the method 500.

In one or more embodiments of the present disclosure, the step of the method 500 scanning S1 and/or the step of estimating S4 occurs before and/or after the step of supplying Sx2 resin, or before and/or after the step of curing Sx 3.

Fig. 7 shows a block diagram illustrating an exemplary fiber misalignment detection arrangement 700 according to some aspects of the invention. The fiber misalignment detection apparatus 700 includes an x-ray beam emission module 701 configured to scan the elongated structure along at least a portion of the length by emitting an x-ray beam at an angle compared to the longitudinal direction. The x-ray beam emission module 701 is for example an x-ray tube or an x-ray generator module capable of transmitting an x-ray beam or signal through an elongated structure. The x-ray beam emitting module 701 is, for example, configured to emit an x-ray beam at an energy level in the range of 5keV-120 keV. The x-ray emission source may be operated at 40-100 muA. In one or more embodiments, the x-ray beam emission module 701 includes a collimator 701a, and the x-ray beam emission module 701 is configured to scan the elongated structure along at least a portion of the length by emitting an x-ray beam through the collimator 701a at an angle compared to the longitudinal direction (e.g., at an angle compared to a line or plane formed by the collimator 701 a). The collimator 701a may be a slit collimator.

The fiber misalignment detection apparatus 700 includes an x-ray detector module 703 configured to detect scattered radiation. The x-ray detector module 703 may include a detection medium, such as a forward scatter and/or backscatter detection module, capable of detecting the resulting pattern (and radiation) of the scan.

The fiber misalignment detection apparatus 700 includes a processing module 702 configured to: determining the intensity of the detected scattered radiation; and estimating a magnitude of the fiber misalignment based on the determined intensity. The processing module 702 includes, for example, an intensity determiner module 702a configured to determine an intensity of the detected scattered rays and an estimator module 702b configured to estimate a magnitude of the fiber misalignment based on the determined intensity. The fiber misalignment detection apparatus 700 may further include an interface module configured to receive and transmit fiber misalignment information and a memory module configured to store the fiber misalignment information and/or scans related to position (of scanned fiber layers or x-ray systems) in order to provide an overall view of the blade and possible positions of fiber misalignment. The fiber misalignment information may then be compiled by the processing module 702 to generate a report or map that maps fiber misalignment above a certain threshold for requirements for the elongated structure. When the elongated structure is a wind turbine blade, then fiber misalignment above a certain threshold is mapped against an acceptance criterion regarding the relationship of misalignment magnitude to strain level. It is envisaged that the critical magnitude of fibre misalignment may be derived from the strain level of each cross-section of a known wind turbine blade. This may allow to ensure a safe reserve level for each manufactured blade.

FIGS. 8a-b show a view of an in-sweepA diagram of exemplary fiber

misalignment detection devices

800a, 800b according to embodiments of the invention while describing an elongated structure 300. The

devices

800a, 800b are configured to slide along the elongated structure 300, for example in suspension. The

apparatus

800a, 800b comprises an x-ray beam emission module 801 configured to emit x-rays through a beam in a direction compared to a longitudinal directionDEmits an x-ray beam to scan the elongated structure 300 along at least a portion of the length. The x-ray beam emission module 801 includes a collimator 801a in an arrangement 800a and two collimators 801a-b in an arrangement 800 b. The collimator may be a slit collimator configured to generate or shape one or more line beams. The apparatus 800a 800b includes an x-ray detector module (such as one backscatter detector module 803a or two backscatter detector modules 803a 803 b) configured to capture reflected or backscattered radiation. The x-ray detector module may include a detector collimator or pinhole. The backscatter detector module allows one side inspection of the elongated structure, i.e. the source and detector can be placed on one side of the elongated structure. This is advantageous for large and complex elongated structures. Imaging-based backscattering measures the intensity of scattered radiation associated with the density of elongated structures and thus improves accuracy in multi-material elongated structures. The backscatter detection module 803a may include a plurality of detector sub-modules 8031.

The

apparatus

800a, 800b is configured to determine or measure the intensity of the reflected or backscattered radiation and estimate the magnitude of the fiber misalignment based on the intensity.

The

devices

800a, 800b may be placed in a shielded box.

In an exemplary setup, to which the proposed technique is applicable, this setup uses a primary beam shaped by a slit collimator. Such a linear beam passes through the sample and generates a scattered beam across the thickness of the elongated structure. The scattered beam is then projected by a pinhole collimator to an x-ray detector module. The distance of the elongated structure from the emission point of the x-ray tube is set to 5-25 cm. The distance of the pinhole is set to 5-25 cm. The slit width of the collimator is set to 0.1-1mm and the pinhole diameter is set to 0.1-1 mm. The x-ray tube was operated at 80kV and 150 μ a (power of 12W). A typical measurement of a single backscatter image of the cross section of the elongated structure can obtain 100-10000 frames at an exposure time of 0.01-10 ms. The frame is analyzed and a spectral image is generated. The detector operates in a spectral measurement mode that measures the energy of each detected X-ray photon. The resulting pattern can be formed from 250 tens of thousands of detected photons.

The invention has been described with reference to the preferred embodiments. However, the scope of the present invention is not limited to the illustrated embodiments, and variations and modifications may be implemented without departing from the scope of the present invention.

Claims

1. A method for detecting fibre misalignment in an elongated structure having a length along a longitudinal direction and comprising a plurality of stacked layers of reinforcing fibres, wherein the plurality of stacked layers of reinforcing fibres comprise fibres having an orientation substantially unidirectionally aligned in the longitudinal direction, wherein the method comprises the steps of:

a) scanning the elongated structure along at least a portion of the length by emitting an x-ray beam at an angle compared to the orientation of the fibers,

b) the scattered radiation is detected and the scattered radiation is detected,

c) determining the intensity of the detected scattered radiation, an

d) Estimating a magnitude of the fiber misalignment based on the determined intensity.

2. The method of claim 1, wherein scanning the elongated structure along at least the portion of the length comprises moving a fiber misalignment detection device comprising an x-ray beam emission module and an x-ray detector module along at least the portion of the length of the elongated structure.

3. The method according to any of claims 1-2, wherein the angle is an angle between about 0.5 degrees and about 45 degrees with respect to a plane of the fiber layer.

4. The method according to any of claims 1-2, wherein the angle is an angle between about 0.5 degrees and about 15 degrees with respect to a plane of the fiber layer.

5. The method of any of claims 1-2, wherein emitting the x-ray beam at the angle comprises emitting the x-ray beam through a collimator and/or emitting the x-ray beam at low power.

6. The method of any of claims 1-2, wherein the method further comprises scanning the elongated structure along at least a portion of the length by emitting additional x-ray beams at additional angles.

7. The method of any of claims 1-2, wherein estimating a magnitude of the fiber misalignment based on the determined intensity comprises determining whether the determined intensity is above an intensity threshold, and detecting a fiber misalignment to repair when the determined intensity is determined to be above the intensity threshold.

8. The method of any of claims 1-2, further comprising positioning fiber misalignment within the elongated structure to effect repair.

9. The method according to any of claims 1-2, wherein the scanning and/or estimating occurs before and/or after an infusion phase before and/or after the curing phase, in which infusion phase resin is infused on the fibre layers forming the elongated structure.

10. The method according to any one of claims 1-2, wherein the plurality of stacked reinforcement fiber layers comprises carbon fiber layers, or carbon fiber layers and glass fiber layers.

11. The method according to any one of claims 1-2, wherein the plurality of stacked reinforcement fiber layers comprises a carbon fiber layer with tracer yarns.

12. The method according to any one of claims 1-2, wherein the plurality of stacked layers of reinforcing fibers comprises 1 to 60 layers.

13. The method according to any of claims 1-2, wherein the elongated structure is a wind turbine blade component, and wherein the wind turbine blade component is a load bearing structure.

14. A method of manufacturing an elongated composite structure of a fibre composite material comprising reinforcing fibres embedded in a polymer matrix by using a mould having a length in a longitudinal direction, wherein the method comprises the steps of:

i) stacking a plurality of fiber layers in a mold, wherein the plurality of fiber layers comprise fibers having an orientation that is substantially unidirectionally aligned in a longitudinal direction;

ii) supplying the fibrous layer with liquid resin, and

iii) curing the resin to provide an elongate composite structure, characterised in that,

the method comprising the step of detecting fiber misalignment by using any of the methods of claims 1-13.

15. A fiber misalignment detection device, comprising:

-an x-ray beam emission module configured to scan an elongated structure along at least a part of the length by emitting an x-ray beam at an angle compared to the longitudinal direction, wherein the elongated structure has a length along the longitudinal direction and comprises a plurality of stacked layers of reinforcing fibers, wherein the plurality of stacked layers of reinforcing fibers comprise fibers having an orientation substantially unidirectionally aligned in the longitudinal direction;

-an x-ray detector module configured to detect scattered radiation;

-a processing module configured to:

-determining the intensity of the detected scattered radiation; and

-estimating the magnitude of the fiber misalignment based on the determined intensities.

16. The fiber misalignment detection apparatus of claim 15 wherein the x-ray beam emission module comprises a collimator, and wherein the x-ray beam emission module is configured to scan the elongated structure along at least a portion of the length by emitting an x-ray beam through the collimator at an angle compared to the longitudinal direction.